Multiple stage pumping system



Jan. 2, 1945. M A, CROSBY 2,366,388

MULTIPLE STAGE PUMPING SYSTEM Filed April 29. 1942 44, 43 42,4' 4 \s 4v 33p- 45 la v. D. I3

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a Y. .t c l Jinx] I i v' su." j, 'l, I l INVENToR V D' Maqvm ACROSBY ATORNEYb Patented Jan. 2, 1945 UNITED STATES MULTIPLE STAGE PUMPING SYSTEM Melvin A. Crosby, Dayton, ohio; signor to The Hydraulic Development Corp. Inc., Wilmington, Del., a corporation of Delaware Application. April 29, 1942, Serial No. 440,947

3 Claims.

This invention relates to a uid supply system for placing fluids under pressure and for delivering the uids to a fluid actuated apparatus. Specically, the invention relates to a pumping system for placing liquid under pressure which is supplied to a hydraulically actuated apparatus.'

An object of the invention is to provide a uid pressure system which is capable of delivering large volumes of fluid at low pressure and relatively smaller volumes of fluid at high pressure while utilizing the full output of the complete pumping system.

It is another object of the vinvention to provide a uid pumping system which can supply a large volume of lowpressure fluid or a somewhat smaller volume of high pressure fluid without bypassing any of the output of the system when shifting from delivery of a large volume low pressurev iiuid to a low volume high pressure fluid.

It is another object of the invention to provide a uid pumping system utilizing a plurality ofv pumps for delivering their uid in parallel until a predetermined pressure is reached in the system. and then shifting the arrangement of the pumps so that they will deliver in vseries and thereby permit the' production of a much higher uid pressure. A

Another object of the invention is to provide a liquid pumping system utilizin-g a plurality of pumps wherein the delivery from the pumps is in parallel until va predetermined pressure is reached. after which one of the pumps maintains the predetermined pressure upon another of the pumps -for delivering the liquid through the plurality of pumps in series so that the Dressure diierential between the inlet and outlet of the pumps will not be carried above the pressure developed in the system when the pumps Were operating in parallel.

Another object of the invention is to provide a fluid pumping system utilizing a plurality of pumping units associated with one another in a manner that one of the pumping units maintains a predetermined pressure upon another ofthe pumping units so that said other pumping unit will produce a predetermined pressure differential across the unit regardless of the pressure of the uid admitted to the unit.

Another object of the invention is to provide a plurality of variable delivery pumps associated with one another in a manner that the pumps will deliver a fluid under pressure in parallel until a predetermined pressure is reached, after which the pumps will be arranged in series sov that one of the pumps will supply fluid under pressure to the other of the pumps whereby the pump being supplied with fluid under pressure can operate to increase the pressure in the delivery portion of the system without causing any 5 increase in pressure differential over that established prior to the change from parallel flow to series flow.

Another objectY of the invention is to provide a pumping system in accordance with the foregoing object wherein the change-over from parallel to series ilow of the pump units is accomplished automatically 'and in response to the pressure in the pumping system.

It is another object of the invention to provide a fluid delivery system using a pair of variable delivery pumps associated with one another in a manner that the pumps will deliver either in parallel or series flow arrangement whereby the system can supply a large volume of low pressure -fluid when the pumps are in parallel arrangement and a small .volume of high pressure fluid when the pumps are in series arrangement without materially effecting the bearing load of the pumps regardless 'of whether they are .in series or parallel iiow arrangement.

Another object of the invention is to provide a iiuid delivery system constructed and arranged in accordance with any of the foregoing objects wherein the fluid pumps are of the constant delivery type. I

Another object of the invention is to provide a fluid pressure delivery system wherein thel bearing loads upon the pumping units are not increased above a normal load when using the pump singly, even though the pressure developed by the pumping system is greater than either of the pumps alone could produce without developing abnormal bearing load conditions. l Further objects and advantages will become apparent from the drawing and the following description.

In the drawing: y Figure l is a schematic view of the pumping system of this invention using variable delivery pumps as the sources for developing iiuid pressure.

Figure 2 is a schematic view similar to Figure 1 showing a modified arrangement of the pumping system.

Figure 3 is a schematic view of a pumping system, similar to that disclosed in Figure 1, showing the manner in which constant delivery pumps can bevapplied to the system.

This invention relates to pumping systems for developing fluid pressure and for transmitting the the pressure actuated device.

fluid under pressure to a pressure actuated apparatus. Particularly the invention relates to a pumping system for placing liquid under pressure and for delivering the liquid under pressure to a hydraulically actuated device.

. Many pressure operated devices are required to have different rates of Atravel in various portions of their cycle of operation. In order to vary the rate' of travel of` a pressure operated device which has a substantially constant increase in its volumetric displacement as it moves; it is required to supply a relatively large volume of iiuid to the device. If the device meets with work resistance pressure will build up in the device until the normal capacity of the fluid supplying system is reached.- Thereafter it is many times desirable to increase the pressure ofthe fluid s upplying system to cause the working stroke of the pressure actuated device. v

Normally, this has been accomplished by the use of a single pump delivering pressure fluid to When a single pump is used for supplying the pressure the pressure differential across the pump is from zero to the maximum pressure being developed which thereby imposes a considerable load upon the bearings of the pump. Also, as the pressure within the pump increases the emciency of the pump falls ofi. Therefore the maximum pressure that can be developed by a pump depends considerably upon the load that can be carried by the bearings without causing any harmful result. Such a single pumping system, however, will only have the volumetric displacement of the single pump used.

If, however, the pumping system is arranged so that two or more pumps are placed in series, then the maximum pressure developed by the system is greatly increased, since each of the pumps can develop pressure to its maximum practical limit. The first pump can deliver its fluid at its maximum practical pressure limit into the suction side of the secondpump so that the second pump can deliver fluid at an increased pressure from lthat delivered by the first pump and yet the bearing loads on the second pumpwill not be extremely great because the maximum pressure differential across the second pump will be the same as the maximum pressure diierential across the first pump. Such a system is limited by the volumetric displacement of the second pump.

However, this invention associates a pair of pumps together in a circulatory system in a manner that the advantage of large volume delivery at sirable that the pressure be increased upon the Y ram to overcome the work resistance. At this time the system of this invention will automatically change over from a parallel flow delivery system to a series system for producing the increased pressure without increasing any added load upon the pump units.

In order to set forth the manner in which this invention is used the pumping system is disclosed in combination with a pressure actuated ram III which may be the ram of a hydraulic press, and

will be so described. It is to be understood, how- 1 means of conduits I4 and I5 respectively. 'I'he low pressure is obtained by placing the pumps in parallel flow arrangement and the advantage of high pressure delivery at a somewhat reduced volume is also obtained by placing the pumps in series, the system being constructed4 and arranged with suitable controls for producing the vchange-over automatically. This system therefore has the advantage cf being able to traverse a'pressure operated'dev'ice rapidly until the work resistance met by the device increases to a predetermined maximum, after which the pumping system will automatically change over into a series pumping arrangement for delivering fluid to the -pressure actuated` device at a much higher pressure but at somewhat reduced volume. Such a system is particularly advantageous when used in combination with hydraulically actuated pressing rams wherein the initial part of the stroke of the ram can be carried forward by means of a large volume of fluid under relatively low pressure. When the ram meets work resistance caused by exertion of effort upon-the work it is then devalve 23 is connected by means of a conduit 25- discharge side of the variable delivery pump I I vconnects to the suction side or the variable delivery pump I2 by means of a conduit I8. The conduits I5 and I8 both supply the suction side of the variable deliverypurnp I2 at different times and under different conditions as will be hereinafter described.

A conduit I1 connects the discharge conduit It` of the variable delivery pump II with a supply conduit I8 for a 4-way valve I9. v The pump I2 is provided with a discharge conduit 20 which also yconnects with the supply conduit I8 for the 4- way valve I9.

A check valve 2l is located in the supply ccnduit I'5 for the pump I2 and is adapted to close when pressureuid is supplied to the conduit I5 in a manner hereinafter described. A similar check valve 22 is placed in the conduit Il and is adapted to be closed when pressure in the conduit 20 rises above the pressure in the conduit I1 in a manner which will be hereinafter described. An admission valve 23 is provided in the conduit I8 between the connecting points of conduits I5 and I'I and is normally closed. The admission valve 23 is constructed and arranged in the manner of a conventional pressure operated valve which is actuated to open when pressure is applied upon ythe actuating element of the valve. Such pressure actuated valves which are opened by a predetermined pressure and closed when pressure is released therefrom are well-known in the art and any one of such valves would sufllce as the admission valve 23. 'I'he pressure actuating element 24 of the admission with the conduit 20 so that the valve 23 is opened in response to the pressure existing in the conduit 20.

Fluid directed to the 4-way valve I9 is supplied to the ram I8 through conduits 28 and 21 to opposite ends of a cylinder 28. A piston 29 operates within the cylinder 28 and carries a suitable plunger 30 for moving suitable apparatus for per'- forming work upon various types of material.

The pumps II and I2 are of the variable delivery type as .heretofore mentioned. 'Ihese pumps may be of any conventional construction, such as a vane pump, a radial pump, a roller type pump or any other of the various types of pumps adapted for variable delivery of iluid.

The pump I I is provided with a conventional shift ring 32 for shifting the pumping elements delivery. A'similar shift ring 33 is provided for the variable delivery pump I2.

The shift ring 32 of the pump II has a plunger 34 extending therefrom which engages a spring 35 retained in a casingl 35 for urging the shift ring toward full stroke position whereby the volumetric displacement of the pumping elements of the pump II are positioned attheir maximum displacement. The opposite side of the shift ring 32 is connected to a piston 31 which reciprocates in a cylinder 38. The cylinderv38 is supplied with pressure fluid through 'a conduit 39 connected to the discharge conduit I1 of the pump I I. Pressure inthe cylinder 3'8 urges the shift ring 32' toward neutral position when the pressure in the discharge conduit I1 rises sufficiently high to equal and overcome the resistanceof the spring 3|. The pressure developed by the pump II is thus controlled by its discharge pressure to reduce the delivery of the pump,.when the pressure reaches a predetermined maximum. This discharge pressure can be changed by varying the compression of the spring 35 through means of the adjusting nut 40 which is in engagement with the spring 35.v

The variable delivery pump I2 is provided with a similar control system consisting of the plunger 4I and the spring 4 2 disposed within the casing 43 for urging the shift ring 33 toward full stroke position. A piston 44 working in a cylinder 45 opposes the spring 42 to shift the pump I2 toward neutral when the pressure in the discharge line 20 reaches a predetermined maximum and is transmitted to the cylinder 45 by means of the conduit 46. The discharge pressure of the pump I2 can be changed by varying the compression of the spring 42 by means of the adjusting nut 41.

The spring 42 of the pump l2 is considerably stronger than the spring 45 of the pump Il so that the pump I2 will not be shifted to neutral at the same time shifting would occur in .the

pump II. Assuming that it is desired to produce a fluid pressure of 2000 P. S. I. and that the pumps II and I2 are designed to operate under a maximum pressure differentiall condition of i000 P. S. I. then it carl be seen ,that the spring 42 will need to be twice the strength of the spring 35 With the assumption that the pumps II and I2 are designed to work against a pressure'differential across the pump of 1000 P. S. I. it be# comes apparent that when the pumps are arranged in parallel flow arrangement that the maximum pressure delivered to the ram I0 will be 1000 P. S. I. However, when the dischargel pressure of the pump II is applied upon the suction side of the pump I2 it then becomes apparent that if the suction pressure for pump l2 is 1000 P. S. I. that the discharge pressure of the pump l2 can be.2000 P. S. I. without any increase in the bearing load cf the pump VI2 over that developed when it was working in parallel with pump II. since the pressure drop across the pump is 1000 P. S. I. Since the pressure drop across the pump determines the bearing load and not the total effective pressure developed by the pump it becomes apparent that when the two pumps are arranged in series that the* maximum pressure developed in the system can be greatlyincrea-sed. However, when the pumps are placed in series the volume delivered to the system by vthe pump I2 then fallsto approximately half the allel.

Such an arrangement is advantageous for use upon hydraulic presses wherein a large volume of low pressure fluid is required for a fast traverse of the ram to close upon'the work piece and produce the initial formation on the article being worked on and then as the work resistance builds up it is desirable to increase the pressure upon the ram and slow down its movementso that the work piece can be completely formed by the increased pressure upon the ram The system of this invention accomplishes the automatic change-over from large volume low pressure to small volume high pressure delivery automatically. As heretofore mentioned, the admission valve 23 is normally closed. Therefore, when the pumps begin to supply uid through the 4-way valve I9 to the press ram .III through the conduit 26' both pumps II and I2 will have their suction sides connected to the supply tank I3 through the conduits I4 and I5, respectively. 'I'he discharge from these pumps will be through conduits I1 and 20 respectively and the total volume displaced by both pumps l I and I2 will be supplied to the supply conduit 26 and thus-to the ram I0. A large volume of low pressure is therefore supplied td the ram for rapidly advancing the same. As the Work resistance increases the pressure in Athe discharge conduits l1 and 20 of the pumps II and I2 respectively increases until the maximum pressure for which the pumps were designed has been reached, namely, our assumed figure of 1000 P. S. I. At this time the admission valve 23 will open because the pressure in the conduit 20 is supplied to the actuating ele- I ment 24 of the admission valve 23 through the conduit 25, and the admission valve has been designed or adjusted so that it will open when the pressure in the conduit 20 reaches 1000 P. S. I.

When the admission valve 23 opens uid under pressure of 1000 P. S. I. is supplied from the pump Il to the suction side of pump I2, thereby closing check valve 2l. Since the Work resistance continues to build up against the ram I 0 the pressure in conduit 20 increases above the 1000 P. S. I.

` existing in conduit I1 and thereby closes check valve 22. The pump I2 now receiving its suction fluid at 1000 P. S. I. can increasethe pressure of that fluid to 2000 P. S. I. and discharge the same through conduit 20 to the ram I0. The load carried by the pump l2 in increasing the pressure from 1000 P.S. I. to 2000 P. S. I. is 1000I P. S. I.

. Therefore, the two pumps in series can produce a higher pressure than either ofthe pumps singly.`

'I'he automatic change-over from parallel flow arrangement of the pumps Il and I2 to the series flow arrangement is accomplished solely by the opening of the admission valve 23.

It. has previously been mentioned that the spring 42 is twice the strength of the spring 35. This is provided so that the pump I2 will not shift to neutral before the pressure in conduit 20 reaches the maximum pressure capable of being developed in this system.

The pump I I is designed with a slightly greater -displacement than the pump I2 to insure a positive pressure in the suction side of the pump I2 when the pumps are in series arrangement Since the spring 35 controls the pressure developed by the pump II the capacity of the pump II will be matched exactly tothe capacity of the pump I2 because any pressure increase above 1000 P. S. I. will tend to shift the pump I I toward neutral, whereby its delivery capacity will be delivery `when the pumps were working in par-V In Figure 2 there is shown a modiiled arrange-v righthand end of the control piston a is greater thanthe pressure ontheletthandend ofthe control piston a byan amount equal to or greater ment of the duid pumping system of this invention that is somewhat similar to the system disclosed in Figure 1 so that the elements of Figure 2 that are identicalwith the elements of Figure 1, und serve the same purpose, will bereferred to by the same numeral as indicated in Figure 1 but with the sumx 41.

In this modification the pump Ila is provided with a control spring 35a opposed by a control piston 21a for shifting the pump lla between full stroke `and neutral position. l'l'he pump l2a is provided with a control Spring 42a and a control piston a for shifting the pump Ila between full stroke and neutral position. The conduit 25a for the admission valve 23a is provided with a manually operated shut oil? valve l to prevent transmission of pressure from the conduit 20a t0 the pressure actuating element 24a for the admission valve 23a. When the valve '58 is closed the pumps l la and I2a will operate continuously on high vvolume low. pressure delivery -since the admission vvalve 23a cannot open to permit the pumps Ila and Ila to be interconnected in series arrangement.

One side of the control piston a for the pump lla is connected to the discharge conduit 25a of the pump |2a by means of the conduit 45a whereby the control piston a urges the shift ring 33a to neutral position when the pressure in the conduit 25a reaches the' compression resistance of the spring 42a.

To aid the spring 52a in its control function a conduit 55 connects the suction'conduit I5a between the pumps lla and I2a with the control cylinder 45a of the pump Ila, the conduit 50 entering the cylinder 45a on the opposite side of the control piston a from that assumed by the conduit lia. Therefore, the pressure in the suction conduit I5a is transmitted to the lefthand end of the control piston a when the admission valve 23a is open so that the pressure in the suction conduit IBa vadds its eilect to the control spring 42a.

When the admission valve 23a and the pumps I la and l2a are operating, the discharge from the pumps will be in parallel in the manner heretofore disclosed with regard to Figure l. As the work resistance met by the ram Ilia` increases the pressure in the discharge conduits Ila and 25a increases until the admission valve 23a opens in the manner -heretofore `described with regard to Figure l. When the admission v alve 25a opens the discharge pressure of the pump Ha is applied force in the modiiication shown in Figure 2 so* that when the pumps are arranged in parallel arrangement they will both be shifted to neutralV when the pressure in thedischarge conduits of the pumps reaches the maximum pressure for which the pumps were designed.

than the ettect of the spring 52a whereupon the s hift ring 53a will be shifted to neutral." Regard- .less of what pressure is-applied upon the suction side of the pump I2a by the-pump Ila the pressure increase developed by the pump I2a will be equal to the setting of the spring 42a so that it can always maintain al predetermined pressure diilerential'between the inlet and outlet thereof.

Aside from the Ilmctioning of the control element for the pmnp I2a the system disclosed in Figure 2 functions in the. same manner as heretofore described with regard to Figure l.

In Figure 3 there isshown another slightly modiiied arrangement or the duid pressure sysy tem of this invention wherein constant delivery upon the suction side of the pump 12a and is.

pumps are used for producing either a large volume low pressure delivery or a small volume high pressure delivery. Inthis modication the constant delivery pumps 5l and 52 receive nuid from the storage tank 53 by means of conduits 54 and 55 respectively. The discharge conduits 55 and.

51 respectively from the pumps 5I and 52 deliver iluid to a supply conduit 58 which connects to a 4- way control valve 59 having supply conduits 50 and 5I which connect to a suitable pressure operated device. A conduit connects the discharge conduit 55 of the pump 5| with the suction conduit 55 of the pump 52. The conduit 52 has an admission valve 55 therein responsive to the pressure in the discharge conduit 51 of the pump 52 through means of a conduit 64. A check valve 55 is disposed in the conduitl 55 to prevent pressure iiuid from iiowing from conduit 51 into conduit 55. A similar check valve is vprovided in the suction conduit 55 for the pump 52 to prevent ow of pressln'eY iluid from the conduit. 52 into the storage tank 53. A pressure relief valve 51 is placed in by-pass line 58 which connects the discharge conduit 55 for the pump 5I with the iiuid storage tank 5 3 and is set toopen when the pressure in the discharge conduit 56 is equal to the maximum pressure forwhich the pump 5I was designed to deliver. a

vA similar pressure relief valve 59 is'placed in the by-pass line Il for the pump 52 to discharge pressure uid from the pump '52 to the storage tank 53-when discharge pressure of the pump 52 rises to the maximum for which the pump was designed to produce.

i due to the increased work resistance met by th However, when the discharge pressure from the pressure operated device, the pressure will open the admission valve 53 when a predetermined maximum pressure is reached in the discharge conduits 55 and 51.

When the admission valve 53 opens the check valves 55 and 55 close whereby the pressure fluid delivered by the pump 5I will be directed into the suction side oil the pump 52, whereby the pump 52 can incree the pressure( delivered in the same manner as heretofore described in Figure 1, referring to pump I 2.

The pump 5I will be of slightly greater capacity than the pump 52 to insure positive pressure being retained upon the suction side oi the pump l aseass's in.. When the pressure in the discharge conduit Il. for the pump I tends to rise because of its greater delivery thenthe pressure relief lvalve i1 Y paratus can be modified without departing'from the spirit of the invention and that such modification'as'fall within thetscope' of vthe appended claims are intended'to be included herein.

' Having thus fully described my invention, what I claimas new and desire to secure by Letters Paten't,is: Y

1. A uid pressure system including a plurality of pumping elements, conduit means connecting the discharge4 side of said pumping elements for parallel discharge iiow, conduit means connecting the discharge side of one o i' the pumping elements with the intake vside 'of another ofthe pumping elements having uid flow control'means therein responsive to the discharge pressure of the pumping elements when in parallel flow arrangement to open the conduit means controlled thereby when the parallel ow discharge pressure reaches a predetermined `maximum and place Vingthe pumps into series flow arrangement upon development of a determined maximum pressure in the uid pressure system not Agreater than the Vmaximum capable of being delivered by the pumps. one yof said pumps delivering fluid under prsure into the other of said pumps when in series flow arrangement whereby said other pump can increase the maximum pressure developed in the pumping in series now arrangement,

and individual control means foreach of said pumping elements responsive solely to the discharge pressure developed by the element for regulating the maximum pressure developedY thereby, the control element for the pumping unit receiving discharge pressure from the other pumping unit `when in seriesow arrangement having means responsive to the fluid pressure in the conduit interconnecting the pumping units in series ilow arrangement for increasing the range of operation ot the control element by an amount equal to the fluid pressure in said interconnecting conduit.

2. A uid pressure system including a pair of variable delivery pumps, individual pressure actuated means for regulatingl the stroke of each of the pumps and thus controllingthe maximum pressure developed by each of the variablerdelivery pumps to a predetermined amount from a zero pressure setting, conduit meansv interconnecting said pumps inseries or parallel flow arrangement, and meansl Iactuated solely by the pressure in the uid pressure systemwhen the pumps are in` parallel iiow arrangement for shiftthe nuid pressure system to a pressure substan- I tially greater than the pressure at which it receives its inlet iiuid, and means connecting said control means for said high pressure pump to the inlet pressure for said pumpwhereby to raise the pressure setting of said control means by an amount equal to the iiuid pressure existing on the inlet side of said pump to maintain control of the pressure diierential across said pump not greater than when said pump was operating in parallel with the pump now delivering uid unde pressure thereto.

3. A fluid pressure system including a plurality of pumping elements, conduit means connecting the discharge side of said pumping elements for elements operable at the sameeiective operating pressure and responsive solely to vthe discharge pressure developed by the element that it is to control for regulating the maximum pressure developed thereby, the control element for the pumping unit receiving discharge pressure from the other pumping unit when in series ow arrangement having means responsive to the uid pressure in the conduit interconnecting the pumping units in seriesfiow arrangement for increasing the range of operation of the control element by an amount equal to the fluid pressure in said interconnecting conduit, and means A for rendering the said discharge pressure eiecl tive or ineffective on the said control unit to obtain selective operation of said pumping elements either in parallel or in series ow arrangement.

MELVIN A. CROSBY. 

